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Subject: sched: Add saved_state for tasks blocked on sleeping locks
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sat, 25 Jun 2011 09:21:04 +0200
Spinlocks are state preserving in !RT. RT changes the state when a
task gets blocked on a lock. So we need to remember the state before
the lock contention. If a regular wakeup (not a RTmutex related
wakeup) happens, the saved_state is updated to running. When the lock
sleep is done, the saved state is restored.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/sched.h | 2 ++
kernel/sched/core.c | 31 ++++++++++++++++++++++++++++++-
kernel/sched/sched.h | 1 +
3 files changed, 33 insertions(+), 1 deletion(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1378,6 +1378,7 @@ struct tlbflush_unmap_batch {
struct task_struct {
volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
+ volatile long saved_state; /* saved state for "spinlock sleepers" */
void *stack;
atomic_t usage;
unsigned int flags; /* per process flags, defined below */
@@ -2483,6 +2484,7 @@ extern void xtime_update(unsigned long t
extern int wake_up_state(struct task_struct *tsk, unsigned int state);
extern int wake_up_process(struct task_struct *tsk);
+extern int wake_up_lock_sleeper(struct task_struct * tsk);
extern void wake_up_new_task(struct task_struct *tsk);
#ifdef CONFIG_SMP
extern void kick_process(struct task_struct *tsk);
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1949,8 +1949,25 @@ try_to_wake_up(struct task_struct *p, un
*/
smp_mb__before_spinlock();
raw_spin_lock_irqsave(&p->pi_lock, flags);
- if (!(p->state & state))
+ if (!(p->state & state)) {
+ /*
+ * The task might be running due to a spinlock sleeper
+ * wakeup. Check the saved state and set it to running
+ * if the wakeup condition is true.
+ */
+ if (!(wake_flags & WF_LOCK_SLEEPER)) {
+ if (p->saved_state & state)
+ p->saved_state = TASK_RUNNING;
+ }
goto out;
+ }
+
+ /*
+ * If this is a regular wakeup, then we can unconditionally
+ * clear the saved state of a "lock sleeper".
+ */
+ if (!(wake_flags & WF_LOCK_SLEEPER))
+ p->saved_state = TASK_RUNNING;
trace_sched_waking(p);
@@ -2083,6 +2100,18 @@ int wake_up_process(struct task_struct *
}
EXPORT_SYMBOL(wake_up_process);
+/**
+ * wake_up_lock_sleeper - Wake up a specific process blocked on a "sleeping lock"
+ * @p: The process to be woken up.
+ *
+ * Same as wake_up_process() above, but wake_flags=WF_LOCK_SLEEPER to indicate
+ * the nature of the wakeup.
+ */
+int wake_up_lock_sleeper(struct task_struct *p)
+{
+ return try_to_wake_up(p, TASK_ALL, WF_LOCK_SLEEPER);
+}
+
int wake_up_state(struct task_struct *p, unsigned int state)
{
return try_to_wake_up(p, state, 0);
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1100,6 +1100,7 @@ static inline void finish_lock_switch(st
#define WF_SYNC 0x01 /* waker goes to sleep after wakeup */
#define WF_FORK 0x02 /* child wakeup after fork */
#define WF_MIGRATED 0x4 /* internal use, task got migrated */
+#define WF_LOCK_SLEEPER 0x08 /* wakeup spinlock "sleeper" */
/*
* To aid in avoiding the subversion of "niceness" due to uneven distribution
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